Composite barrier/etch stop layer comprising oxygen doped SiC and SiC for interconnect structures

ABSTRACT

A dual damascene structure comprising a composite barrier/etch stop layer including a lower silicon carbide (SiC) layer and an upper first oxygen doped SiC layer formed over a substrate is provided. A first dielectric layer is formed over the first oxygen doped SiC layer followed by a second oxygen doped SiC etch stop layer, and a second dielectric layer. An opening with a via and an overlying trench extends through the second dielectric layer, the second oxygen doped SiC etch stop layer, the first dielectric layer, the upper first oxygen doped SiC layer and at least a portion of the lower silicon carbide (SiC) layer. The opening is filled with a diffusion barrier layer and a metal layer.

This is a Divisional application of U.S. patent application Ser. No.10/785,520, filed on Feb. 24, 2004, now U.S. Pat. No. 7,052,932 which isherein incorporated by reference in its entirety, and assigned to acommon assignee.

FIELD OF THE INVENTION

The invention relates to the field of fabricating integrated circuitsand other electronic devices and in particular to a dual damascenestructure with high performance and improved reliability and a methodfor forming the same.

BACKGROUND OF THE INVENTION

The manufacture of an integrated circuit in a semiconductor deviceinvolves the formation of a metal layer that typically contains a wiringpattern which is overlaid on another conductive pattern. This process isrepeated several times to produce a stack of metal layers. Metalinterconnects which form horizontal and vertical electrical pathways inthe device are separated by insulating or dielectric materials toprevent crosstalk between the metal wiring that can degrade deviceperformance by slowing circuit speed. A popular method of forming aninterconnect structure is a dual damascene process in which vias andtrenches are filled with metal in the same step. A single damasceneprocess is also commonly employed to form a metal pattern in one or moredielectric layers. The most frequently used dual damascene approach is avia first process in which a via is formed in a stack of dielectriclayers and then a trench is formed above the via. Recent improvements indual damascene processing include lowering the resistivity of the metalinterconnect by switching from aluminum to copper and reducing thedielectric constant (k) of insulating materials to avoid capacitancecoupling between the metal interconnects.

Current manufacturing practices involve forming vias and trenches thathave sub-micron dimensions which can be less than 0.25 microns in width.One of the more promising low k dielectric materials is organosilicateglass (OSG) also known as SiCOH which is a silicon oxide that is dopedwith carbon and hydrogen atoms. Silicon oxide which has beentraditionally used as a dielectric material has a dielectric constant ofabout 4. SiCOH has a k value between about 2 and 3 and thereby providesa much needed reduction in capacitance coupling between wiring. SiCOH isavailable as Black Diamond™ from Applied Materials, CORAL™ fromNovellus, or can be obtained by different trade names from othermanufacturers. The composition and properties of SiCOH may varydepending on the deposition conditions and source gases.

One concern with using SiCOH in a damascene structure is that thematerial as deposited is porous. A porous structure will allow moistureuptake which increases the dielectric constant and defeats the purposeof depositing a low k dielectric material. An organosilicate glass layeris employed as a thick dielectric layer in U.S. Pat. No. 6,472,333. ASiC cap layer is formed on the organosilicate glass (SiCOH) layer toprovide increased hardness for a subsequent chemical mechanical polish(CMP) step and then the SiCOH layer is annealed for improved mechanicalproperties and a lower k value. An amorphous carbon cap layer on a low kdielectric layer is described in U.S. Pat. No. 6,541,397 and serves asan etch mask and as a CMP stop layer.

In some cases, densification after annealing is desirable. A well knownmethod of densifying a porous SiCOH layer is to perform a plasmatreatment such as the N₂/NH₃ plasma process described in U.S. Pat. No.6,436,808. Besides stabilizing the dielectric constant, thedensification also improves SICOH resistance to etchants such as O₂plasma during removal of a photoresist mask that is used to transfer atrench pattern into the damascene stack.

The integration of amorphous silicon carbide (α-SiC:H) as a barrier/etchstop layer in a copper damascene fabrication scheme has been suggestedas a possible solution to the problems of parasitic capacitance and RCdelay in ultra-large scale integration. Although the α-SiC:H film has alower dielectric constant (k˜4.5) than silicon nitride (k˜7), α-SiC:Hhas a higher current leakage level under high bias and a lower breakdownfield than silicon nitride. Nitrogen doped SiC (SICN) has been used as abarrier layer in a damascene structure as mentioned in U.S. Pat. No.6,436,824. While SiCN can improve the leakage performance, trace amountsof amines in SiCN have a tendency to poison a photoresist layer in a viahole during patterning of a trench opening in a via first dual damascenescheme. As a result, photoresist residue remains in the via afterexposed regions are developed in an aqueous base solution which leads toan expensive rework process. In addition, the dielectric constant ofSiCN (k˜4.9) is higher than the desired value of less than 4 andpreferably less than 3 for a low k dielectric material. Therefore, animproved barrier layer or etch stop layer is required for newtechnologies which has a higher breakdown field and lower dielectricconstant than current materials and which does not contain nitrogen thatcan have a deleterious effect on photoresist patterning.

One prior art method that mitigates the poisoning effect of a SiCN etchstop layer is described in U.S. Pat. No. 6,455,417 where a compositeetch stop comprised of an upper carbon doped oxide (SiCOH) is formedover a lower SiCN layer on a substrate. The lower layer acts as a bufferto keep the oxide layer from oxidizing the underlying conductive metalwhile the SiCOH layer prevents the photoresist poisoning issue. However,this prior art does not address the issue of a relatively high k valuefor SiCN and a thick SiCOH layer may be necessary to prevent amines inSiCN from diffusing through the porous upper layer.

Other low k dielectric materials such as benzocyclobutene or hydrogensilsesquioxane (HSQ) are employed as an etch stop layer in a damascenestructure in U.S. Pat. No. 6,417,090. However, there is no provision toform a buffer layer between the oxygen containing HSQ layer and anunderlying copper pattern.

A carbon doped silicon oxide layer is formed on a substrate in U.S. Pat.No. 6,410,462 and uses silane, an oxygen source, and a mixture of CH₄and acetylene for the deposition step. The introduction of methane andacetylene into the CVD process is claimed to promote a lower filmdensity by forming more Si—O network terminating species. In this case,the composition of the SiCOH film appears to be less crosslinked than isnormally desired and may result in a less mechanically sturdy structure.Low density also implies a higher porosity that can lead to waterabsorption and higher k value in subsequent processing steps.

An oxygen or nitrogen doped SiC layer is employed as an etch stop layerin U.S. Pat. No. 6,486,082. However, the concentration of the dopant isnot described.

A method of incorporating a SiCOH layer with a low oxygen content,hereafter referred to as oxygen doped silicon carbide, as an etch stopor barrier layer in a dual damascene scheme is desirable so that areduction in dielectric constant and a higher breakdown field can beachieved without compromising Cu barrier capability or a photoresistprocessing step. An oxygen doped silicon carbide etch stop layer shouldhave good etch selectivity to other low k dielectric layers includingSiCOH layers like Black Diamond™ from Applied Materials or CORAL™available from Novellus.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a method of forminga dual damascene structure with a barrier/etch stop layer comprised ofoxygen doped silicon carbide that has a dielectric constant of about 4or less.

A further objective of the present invention is to provide an oxygendoped silicon carbide barrier/etch stop layer that has a betterbreakdown field than a silicon carbide layer.

A still further objective of the present invention is to integrate anoxygen doped silicon carbide barrier/etch stop layer into a damascenestructure so that oxidation of an underlying metal layer is avoided.

Yet another objective of the present invention is to provide an oxygendoped silicon carbide layer that has good etch selectivity to other lowk dielectric films including Black Diamond™ and CORAL™ and that has goodcopper barrier capability.

These objectives are achieved by providing a substrate having a firstmetal layer with an exposed top surface. The first metal layer may beformed in an opening that is lined with a diffusion barrier layer. Inone embodiment, the first metal layer and diffusion barrier layer arecontained in a first dielectric layer that has an overlying siliconcarbide (SiC) cap layer which is coplanar with the first metal layer. Asecond SiC layer may be formed on the substrate to form a protectiveetch stop barrier over the first metal layer. Next, a first oxygen dopedSiC layer is deposited on the SiC barrier layer by a plasma enhancedchemical vapor deposition (PECVD) process and also functions as abarrier/etch stop layer. The first oxygen doped SiC layer may be furtherprocessed by treating with a plasma comprised of an inert gas such asHe, Ar, or N₂ to densify the layer and prevent any increase indielectric constant. A second dielectric layer is deposited on the firstoxygen doped SiC layer followed by formation of a second oxygen dopedSiC layer on the second dielectric layer. The second oxygen doped SiClayer serves as a second etch stop layer and is deposited in a mannersimilar to the first oxygen doped SiC layer. The second oxygen doped SiClayer may also be densified with a plasma treatment. A third dielectriclayer is deposited on the second oxygen doped SiC layer followed byformation of a cap layer on the third dielectric layer to complete thedamascene stack

A conventional process flow then follows and involves formation of a viapattern in the damascene stack by a photoresist patterning and etchsequence. Similar steps are taken to form a trench pattern in the caplayer and third dielectric layer that is aligned above the via pattern.The exposed first etch stop layer comprised of the second SiC layer andfirst oxygen doped SiC layer is removed to expose a portion of thesurface of the first metal layer. A second diffusion barrier metal layeris deposited on the sidewalls and bottom of the trenches and via holes.Next, a second metal layer is deposited to fill the via and trenchopenings to a level above the cap layer. A planarization method such asa chemical mechanical polish (CMP) process is then employed to lower thesecond metal layer to a level that is coplanar with the cap layer on thedamascene stack to complete the damascene sequence.

The invention is also a damascene structure that is formed on asubstrate that may contain a first metal layer with an exposed topsurface. The damascene structure has a first barrier/etch stop layerthat is a composite of a lower SiC layer and a first oxygen doped SiClayer on the SiC layer. There is sequentially formed on the first oxygendoped SiC layer a second low k dielectric layer, a second oxygen dopedetch stop layer, a third low k dielectric layer, and a cap layer on topof the damascene stack. The damascene stack has a trench in the caplayer and third dielectric layer which is aligned over a via thatextends from the second etch stop layer through the second dielectriclayer and first barrier/etch stop layer. There is a conformal diffusionbarrier layer on the sidewalls and bottoms of the trench and viaopenings and a second metal layer formed on the diffusion barrier layerthat is coplanar with the cap layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are cross-sectional views depicting a method of employing anoxygen doped SiC layer as a barrier and etch stop layer in a dualdamascene process.

FIG. 6 is a plot showing density vs. sputter time during an ESCAanalysis of an oxygen doped SiC layer that was deposited by a method ofthe present invention.

FIG. 7 is a plot showing breakdown field vs. oxygen flow rate for oxygendoped SiC layers that were deposited using different conditions by amethod of the present invention.

FIG. 8 is a plot showing dielectric constant as a function of oxygenflow rate for oxygen doped SiC layers that were deposited usingdifferent conditions according to a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly useful in forming a dual damascenestructure with high performance and good reliability. Although a viafirst dual damascene process is described, the method of incorporatingan oxygen doped SiC etch stop layer into a damascene stack is equallyeffective for other damascene approaches including a single damascenemethod and a trench first dual damascene process. A first embodiment isdepicted in FIGS. 1-5. The drawings are used for illustrative purposesand are not intended to limit the scope of the invention.

Referring to FIG. 1, a substrate 8 is provided that is typicallymonocrystalline silicon but optionally may be comprised ofsilicon-germanium, silicon-on-insulator, or other semiconductormaterials used in the art. The substrate 8 may further include activeand passive devices (not shown). In the exemplary embodiment, a firstconductive layer comprised of three conductive lines is formed on thesubstrate 8. Alternatively, a first conductive layer may be formed witha different pattern. However, the conductive layer should have anexposed top surface.

A first dielectric layer 10 that is preferably comprised of a low kdielectric material selected from a group including fluorine doped SiO₂,carbon doped SiO₂, hydrogen silsesquioxane (HSQ), methyl silsesquioxane(MSQ), fluorinated polyimide, poly(arylether), or benzocyclobutene isdeposited by a chemical vapor deposition (CVD), plasma enhanced CVD(PECVD), or a spin-on method. Two popular forms of carbon doped SiO₂ areBlack Diamond™ from Applied Materials and COREL™ from Novellus.Additional processing of the first dielectric layer 10 may include ahigh temperature cure or anneal at temperatures of up to 600° C. Apassivation layer 11 preferably comprised of silicon carbide isdeposited by a CVD or PECVD technique and has a thickness between about0 and 1000 Angstroms.

A conventional method is used to form openings in first dielectric layer10 and is typically comprised of patterning a photoresist layer (notshown) on the passivation layer 11 and using the photoresist as a maskwhile transferring the pattern through the passivation layer 11 andfirst dielectric layer 10 by a plasma etch process. A conformaldiffusion barrier layer 12 such as Ta, TaN, TaSiN, Ti, TiN, W, or WNhaving a thickness between 50 and 300 Angstroms is deposited on thesidewalls and bottom of openings in first dielectric layer 10. A firstconductive layer that is preferably comprised of copper is deposited onthe diffusion barrier layer 12 to form the conductive lines 13 a, 13 b,13 c. A planarization step is employed to lower the first conductivelayer so that the conductive lines 13 a-13 c are coplanar with thepassivation layer 11. For example, a chemical mechanical polish (CMP)process may be used. It is understood that the widths of the conductivelines 13 a-13 c are not necessarily equal in size. Similarly, the widthof the first dielectric layer 10 between conductive lines 13 a and 13 band between conductive lines 13 b and 13 c is not necessarily drawn toscale and could be larger or smaller in width than the width of theconductive lines 13 a-13 c.

Referring to FIG. 2, a damascene stack of layers is fabricated byinitially depositing a second SiC layer 14 having a thickness from about50 to 150 Angstroms on the passivation layer 11 and on the conductivelines 13 a-13 c by a CVD or PECVD method. In the preferred embodimentwhere the passivation layer 11 is SiC, the second SiC layer 14 is notdistinguishable from first SiC layer 11 and the combined SiC layers 11,14 in FIGS. 3-5 will be referred to as SiC barrier layer 15.

Returning to FIG. 2, a first oxygen doped SiC etch stop layer 16 ispreferably formed on the second SiC layer 14 by a PECVD process thatincludes O₂ with a flow rate from about 20 to 200 standard cubiccentimeters per minute (sccm), a trimethylsilane or tetramethylsilaneflow rate of 280 to 350 sccm, a helium flow rate of from 700 to 1000sccm with a chamber pressure of from 2 to 8 torr, a RF power of from 100to 1000 Watts and preferably 200 to 600 watts generated with a RFfrequency of 13.56 MHz, and a substrate temperature between 300° C. and400° C. and preferably 350° C. The helium is used to help transport thetrimethylsilane or tetramethylsilane into the chamber. The process ispreferably carried out using an inductively coupled plasma (ICP) sourceor a transformer coupled plasma (TCP) source to enable a higher degreeof control and uniformity during the deposition. Under these conditions,the resulting oxygen doped SiC layer 16 typically has a lower oxygencontent than Black Diamond™ or COREL™ films.

The thickness of the first oxygen doped SiC layer 16 is from 50 to 1000Angstroms and preferably from 150 to 350 Angstroms. In one embodiment,the first oxygen doped SiC layer 16 is subjected to a plasma treatmentknown to those skilled in the art to stabilize the dielectric constantand prevent water uptake. For example, the first oxygen doped SiC layer16 may be subjected to a plasma generated from N₂, He, or Ar to densifythe layer. The plasma treatment is preferably performed in the sameprocess chamber in which the previous PECVD process was carried out.

A second dielectric layer 17 having a thickness of from 2000 to 10000Angstroms is deposited on the first oxygen doped SiC layer 16 by a CVD,PECVD or spin-on method. The second dielectric layer 17 is preferablycomprised of a low k dielectric material and is selected from the samegroup of materials previously described for the first dielectric layer10. A conventional cure or anneal process is typically performed toremove trace amounts of solvents and other low molecular weightcompounds from the second dielectric layer 17. In one embodiment, thedamascene stack is completed at this point.

In the exemplary embodiment, a second oxygen doped SiC layer 18 thatfunctions as an etch stop is preferably formed on the second dielectriclayer 17 by the same method employed to form first oxygen doped SiClayer 16 and has a thickness in the range of 50 to 1000 Angstroms. Inone embodiment, the second oxygen doped SiC layer 18 is treated with aN₂, He, or Ar plasma to densify the layer and stabilize its dielectricconstant during subsequent processes.

A third dielectric layer 19 having a thickness from 1000 to 10000Angstroms is deposited on second oxygen doped SiC layer 18 by a CVD,PECVD, or spin-on method. The third dielectric layer 19 is preferablycomprised of the same low k dielectric material used in the seconddielectric layer 17 and is typically cured or annealed to drive offtrace amounts of solvent and low molecular weight compounds. Thedamascene stack may be completed by deposition of a cap layer 20 with athickness between 0 and 1000 Angstroms. The cap layer 20 is comprised ofa material such as SiC, silicon nitride, silicon oxide, fluorine dopedSiO₂, or silicon oxynitride which is deposited by a CVD or PECVDtechnique. The cap layer 20 is selected for its low removal rate in asubsequent CMP step and for its resistance to scratch and dishingdefects during the polishing process.

Referring to FIG. 3, a via pattern comprised of vias 21 a-21 c is formedin the damascene stack. Vias 21 a, 21 b, 21 c are aligned above theconductive lines 13 a, 13 b, 13 c, respectively, in the first conductivelayer. The patterning method typically involves forming via openings ina photoresist layer (not shown) on the cap layer 20 or on the top layerof the damascene stack and employing the photoresist as a mask totransfer the pattern through the underlying layers by a plasma etchprocess that can have multiple steps. Note that the etch process stopson the first oxygen doped SiC layer 16 and the width of the vias 21 a-21c should not be larger than the width of an underlying conductive line.

In a preferred embodiment, the first oxygen doped SiC layer 16 hasenough selectivity to the second dielectric layer 17 so that a minimumamount of the first oxygen doped SiC layer 16 thickness is lost as theetch transfer step removes the last portion of the second dielectriclayer 17 from the bottom of the vias 21 a-21 c. The etch process isusually not completely uniform and the second dielectric layer 17 may beremoved from some vias faster than from others. For example, the etchrate of the second dielectric layer 17 in the vias 21 a-21 c that are ina dense array may be different than in an isolated via (not shown) inthe same via pattern. The first oxygen doped SiC layer 16 is depositedin the preferred embodiment so that it has good selectivity towardscarbon doped SiO₂ materials in the second dielectric layer 17 such asBlack Diamond™ and COREL™ when a plasma etch generated from C₄F₈ and Argases is employed. Optionally, other fluorocarbons may be used in placeof C₄F₈. Those skilled in the art will appreciate that the gascomposition of the plasma etch through the second and third dielectriclayers 17, 19 may be different than in the plasma etch through the caplayer 20 and through the second oxygen doped SiC layer 18.

In one embodiment, the first and second oxygen doped SiC layers 16, 18are formed with a carbon content of from 17 to 25% and an oxygen contentof from 5 to 15%. In comparison, Black Diamond™ or other SiCOH filmsgenerally have a carbon content of 10 to 15% and an oxygen content of 25to 35%. As a result, an etch rate selectivity of between 6:1 and 10:1 isachieved for SiCOH relative to the oxygen doped SiC layers 16, 18 in anetch process having a plasma chemistry based on C₄F₈ and Ar.

Referring to FIG. 4, a trench pattern that includes trenches 22 a, 22 bis formed in cap layer 20 and in the third dielectric layer 19. Thetrench 22 a is aligned above the via 21 a and may be formed above one ormore other vias (not shown) while the trench 22 b is aligned above via21 c and may be formed above one or more vias in an adjacent region ofthe pattern that is not pictured. This is only one possible embodimentfor a dual damascene scheme and other designs in which a trench patternis overlaid on a via hole pattern are equally useful in the presentinvention as appreciated by those skilled in the art. The trenches 22 a,22 b are formed by a conventional sequence that normally involvespatterning a photoresist layer (not shown) on the cap layer 20 andemploying the photoresist as a mask while the trench openings are plasmaetch transferred through the cap layer 20 and third dielectric layer 19.The photoresist remaining on the cap layer 20 and any organic materialin vias 21 a-21 c including the first oxygen doped SiC layer 16 andsecond SiC layer 15 are then removed by a plasma etch so that conductivelines 13 a-13 c are exposed. Preferably, the SiC layer 15 is removed bya soft etch known to those skilled in the art that does not damage theunderlying conductive lines 13 a-13 c and does not deform the sidewallsof the second and third dielectric layers 17, 19 or the sidewalls of thefirst and second oxygen doped SiC layers 16, 18.

Alternatively, when the second dielectric layer 17 is the top layer inthe damascene stack, then a trench pattern is formed in the seconddielectric layer and is aligned over the via pattern as appreciated bythose skilled in the art.

Referring to FIG. 5, a completed dual damascene structure is shown.Preferably, a second diffusion barrier layer 23 selected from the samegroup as described for first diffusion barrier layer 12 is deposited toa thickness of from 50 to 300 Angstroms on the sidewalls and bottoms ofthe trenches 22 a, 22 b and vias 21 a-21 c. Next, a metal layer 24 thatis copper, Al, Al/Cu or W is deposited by an electroplating method orphysical vapor deposition (PVD), for example, on the second diffusionbarrier layer 23 to a level that is above the top of cap layer 20, oroptionally, above the top layer in the damascene stack. The metal layer24 is preferably planarized by a CMP process to a level that is coplanarwith the cap layer 20 or the top of the damascene stack.

An advantage of the damascene method of the present invention is thatthe first and second oxygen doped SiC layers 16, 18 have a lowerdielectric constant (k˜3.7 to 4.3) than convention etch stops such asSiC (k˜4.5) or SiCN (k˜4.9). Furthermore, there is no nitrogen contentin the oxygen doped SiC etch stop layers 16, 18 which eliminates anyconcern about contamination of photoresist in via holes during thetrench definition step. Other performance advantages are realizedbecause the oxygen doped SiC layer of the present invention has a higherbreakdown field (6 mV/cm) than SiC (3.7 mV/cm) while exhibiting asimilar Cu barrier capability to SiC and SiCN. The relationship betweenbreakdown field and O₂ flow rate during the deposition of oxygen dopedSiC layers 16, 18 is depicted in FIG. 7. Representative values fordielectric constants of the oxygen doped SiC layer 16, 18 formed atvarious O₂ flow rates are shown in FIG. 8.

The present invention is also a damascene structure comprised of one ormore oxygen doped SiC etch stop layers as depicted in FIG. 5 and formedby a method of the first embodiment. Although a dual damascene structureis shown, other damascene schemes including a single damascene structureand a second dual damascene structure stacked on a first dual damascenestructure are also compatible with the integration of oxygen doped SiClayers in a damascene stack in this invention. Moreover, the presentinvention anticipates a variety of damascene structures that includevarious combinations of a trench pattern overlaid on a via pattern.Additionally, the damascene stack may include only the first oxygendoped SiC and a second dielectric layer as the top layer.

A substrate 8 is provided that is preferably monocrystalline silicon butoptionally may be based on silicon-germanium, silicon-on-insulator, orother semiconductor materials used in the art. There is a firstdielectric layer 10 on the substrate 8 that is comprised of a low kdielectric material such as fluorine doped SiO₂, carbon doped SiO₂,hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), fluorinatedpolyimide, poly(arylether), or benzocyclobutene having a thickness inthe range of 1000 to 10000 Angstroms. Within the first dielectric layer10 there is a first conductive layer comprised of the conductive lines13 a-13 c. The first conductive layer is formed on a conformal diffusionbarrier layer 12 that is Ta, TaN, TaSiN, Ti, TiN, W, or WN, for example,that lines the sidewalls and bottoms of the openings in the dielectricstack. The conductive lines 13 a-13 c are preferably comprised of copperand are coplanar with the top of the openings in the first dielectriclayer 10.

The damascene structure includes a first barrier/etch stop layer that isa composite of a lower SiC layer 15 with a thickness between 50 and 150Angstroms and an upper oxygen doped SiC layer 16 having a thickness from50 to 1000 Angstroms. The oxygen doped SiC layer 16 has the followingcomposition: 25 to 35 atomic % Si; 17 to 25 atomic % C; 5 to 15 atomic %O; and 20 to 40 atomic % H. In one embodiment, the bottom of the SiClayer 15 is at a level on the first dielectric layer 10 that is belowthe top of the conductive lines 13 a-13 c. Alternatively, the SiC layer15 is formed on a first dielectric layer 10 that is coplanar with theconductive lines 13 a-13 c. A succession of layers is formed on thefirst oxygen doped SiC layer 16 and includes in order a seconddielectric layer 17, a second oxygen doped SiC etch stop layer 18 with athickness and composition similar to first oxygen doped SiC layer 16, athird dielectric layer 19, and a cap layer 20 on top of the damascenestack. Second and third dielectric layers 17, 19 are selected from thesame group of materials as described for the first dielectric layer 10and have a thickness in a range of 2000 to 10000 Angstroms. The caplayer 20 is from 0 to 1000 Angstroms thick and is SiC, silicon nitride,silicon oxide, fluorine doped SiO₂, or silicon oxynitride.

In the exemplary embodiment, the damascene stack has trenches 22 a, 22 bin the cap layer 20 and third dielectric layer 19 that are aligned overthe vias 21 a and 21 c, respectively, which extend through the first andsecond oxygen doped SiC layers 16, 18, the second dielectric layer 17,and through SiC layer 15. The via 21 a is aligned over the conductiveline 13 a while the via 21 c is aligned over the conductive line 13 c. Athird via 21 b extends through the cap layer 20, second and thirddielectric layers 17, 19, and through SiC layer 15 and first and secondoxygen doped SiC layers 16, 18 above conductive line 13 b. Othertrenches and vias may be present in the damascene stack above substrate8 but are not shown. For example, the trench 22 a may be formed overother vias besides via 21 a and the trench 22 b may be formed over othervias in addition to via 21 c. Moreover, other designs in which a trenchpattern is overlaid on a via pattern is anticipated as describedpreviously.

There is a second diffusion barrier layer 23 with a thickness of 50 to300 Angstroms formed on the sidewalls and bottoms of the trenches 22 a,22 b and vias 21 a-21 c that is selected from the same group ofmaterials as mentioned earlier for the first diffusion barrier layer 12.A metal layer 24 is formed that fills the trenches 22 a, 22 b and vias21 a-21 c and is coplanar with the cap layer 20 and with the top ofsecond diffusion barrier layer 23. The metal layer 24 is preferablycomprised of copper but optionally may be Al/Cu, Al, or W Although theinvention is not limited to a specific size of width for the firstconductive layer and metal layers, the invention is especially effectivein improving the performance of a device where the width of the firstconductive layer and metal layer is less than about 0.25 microns.

An advantage of the damascene structure of the present invention is thatthe first and second oxygen doped SiC layers 16, 18 have a lowerdielectric constant (k˜3.7 to 4.3) than conventional etch stopsincluding SiC (k˜4.5) or SiCN (k˜4.9). Other performance advantages arerealized because the oxygen doped SiC layer of the present invention hasa higher breakdown field (6 mV/cm) than SiC (3.7 mV/cm) while exhibitinga similar Cu barrier capability to SiC and SiCN. The relationshipbetween breakdown field and O₂ flow rate during the deposition of oxygendoped SiC layers 16, 18 is depicted in FIG. 7. Representative values fordielectric constants of the oxygen doped SiC layer 16, 18 formed atvarious O₂ flow rates are shown in FIG. 8.

An example in which an oxygen doped SiC layer is deposited on asubstrate according to the present invention is provided in Example 1.

EXAMPLE 1

A 1 micron thick copper film was deposited on 200 mm silicon wafers byan ECP method. Next, a series of oxygen doped SiC films with a thicknessof 500 Angstroms were deposited on the copper coated wafers in aProducer tool available from Applied Materials (AMAT) by a PECVD processinvolving an oxygen flow rate of from 0 to 200 sccm, a helium flow rateof 800 sccm, a trimethylsilane flow rate of 320 sccm at a substratetemperature of 350° C. with a RF power of 460 Watts generated with a RFfrequency of 13.56 MHz and with a chamber pressure of 3.5 Torr. Thedeposition rate is about 900 Angstroms per minute. The films wereannealed by baking at 400° C. for four hours in a nitrogen ambient.

As shown in FIG. 6, a SIMS analysis of the resulting films was plottedas copper concentration or density in terms of atoms/cm³ vs. sputtertime during the analysis. Curve 40 represents a SiC film deposited withno oxygen flow rate. Curve 41 represents an oxygen doped SiC filmdeposited with a 40 sccm flow rate of O₂ while curves 42 and 43 show theresults from oxygen doped SiC films deposited with O₂ flow rates of 75sccm and 200 sccm, respectively. The films deposited at the three lowerO₂ flow rates (curves 40, 41, 42) tend to have a fairly low copperout-diffusion into the oxygen doped films. However, the oxygen doped SiClayer formed with a 200 sccm O₂ flow rate exhibits a much lowerresistance to block the copper out-diffusion. The inventors havedetermined that an oxygen flow rate of 20 to 75 sccm is preferred atthese conditions because the resulting films have a high enoughresistance to block the copper out-diffusion.

The breakdown field (Mv/cm) of the oxygen doped SiC films as a functionof O₂ flow rate during deposition was determined by an Al dot I-Vmeasurement at 150° C. which is well known to those skilled in the art.FIG. 7 shows that the breakdown field improves rapidly while increasingthe O₂ flow rate to 75 sccm and then has a further slight improvement ata 200 sccm O₂ flow rate. At O₂ flow rates between 20 and 75 sccm, theoxygen doped SiC films have a breakdown field of greater than 4 mV/cmwhich is better than a pure SiC film.

Referring to FIG. 8, the dielectric constants of the various films weremeasured at 1 MHz (Curve 51) by an Al dot I-V test at room temperaturewhich indicates that the dielectric constant becomes lower as the oxygenflow rate increases and changes from about 4.3 at 0 sccm O₂ to 3.7 for a75 sccm O₂ flow rate.

The results obtained from the three different types of analysesdemonstrate that an oxygen doped SiC film deposited at O₂ flow ratesbetween about 20 and 75 sccm has an advantage over a conventional SiClayer (0 O₂ flow rate) in terms of a lower dielectric constant and ahigher breakdown field. Furthermore, the oxygen doped SiC film of thepresent invention has an equivalent capacity to function as a copperout-diffusion barrier.

While this invention has been particularly shown and described withreference to, the preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made without departing from the spirit and scope of this invention.

1. A dual damascene structure comprising: a substrate; a compositebarrier/etch stop layer formed over the substrate, the compositebarrier/etch stop layer comprising a lower silicon carbide (SiC) layerand an upper first oxygen doped SiC layer wherein the upper first oxygendoped SiC layer has a silicon content from about 25 to 35 atomic weight%, a carbon content of about 17 to 25 atomic wt. %, an oxygen content ofabout 5 to 15 atomic wt. %, and a hydrogen content from about 20 to 40atomic wt. %; a first dielectric layer formed over the upper firstoxygen doped SiC layer; a second oxygen doped SiC etch stop layer formedover the first dielectric layer wherein the second oxygen doped SiC etchstop layer has a silicon content from about 25 to 35 atomic weight %, acarbon content of about 17 to 25 atomic wt. %, an oxygen content ofabout 5 to 15 atomic wt. %, and a hydrogen content from about 20 to 40atomic wt. %; a second dielectric layer formed over the second oxygendoped SiC layer; an opening having sidewalls and a bottom, the openingextending through the second dielectric layer, the second oxygen dopedSiC etch stop layer, the first dielectric layer, the upper first oxygendoped SiC layer and at least a portion of the lower silicon carbide SiClayer, the opening comprising a via and a trench located in the seconddielectric layer aligned above sad via; and a conformal diffusionbarrier lining the sidewalls and the bottom of said opening and a metallayer formed on the diffusion barrier layer, the metal layer filling theopening.
 2. The dual damascene structure of claim 1 wherein thesubstrate is comprised of a conductive layer with an exposed top surfaceand the opening is coextensive with a portion of the top surface of theconductive layer.
 3. The dual damascene structure of claim 2 wherein theconductive layer and the metal layer are comprised of copper.
 4. Thedual damascene structure of claim 1 wherein the metal layer has a widththat is less than about 0.25 microns.
 5. The dual damascene structure ofclaim 1 wherein the diffusion barrier layer is comprised of Ta, TaN,TaSiN, Ti, TiN, W, or WN and has a thickness in the range of about 50 to300 Angstroms.
 6. The dual damascene structure of claim 1 wherein thefirst and second dielectric layers are comprised of Black Diamond™,CORAL™, fluorine doped SiO₂, hydrogen silsesquioxane (HSQ), methylsilsesquioxane (MSQ), a fluorinated polyimide, a polyarylether, orbenzocyclobutene.
 7. The dual damascene structure of claim 1 wherein thefirst and second dielectric layers have a thickness in the range ofabout 1000 to 10000 Angstroms.
 8. The dual damascene structure of claim1 wherein the lower silicon carbide (SiC) layer has a thickness in therange of about 50 to 150 Angstroms.
 9. The dual damascene structure ofclaim 1 wherein the first and second oxygen doped SiC layers have athickness between about 50 and 1000 Angstroms.
 10. The dual damascenestructure of claim 1 wherein the dielectric constant of the first andsecond oxygen doped SiC layers is between about 3.7 and 4.3.
 11. Thedual damascene structure of claim 1 wherein a breakdown field of thefirst and second oxygen doped SiC layers is greater than about 4milliVolts/cm.
 12. The damascene structure of claim 1 which is repeateda plurality of times to form a stack of metal layers on said substrate.13. An integrated circuit comprising: a substrate; a compositebarrier/etch stop layer formed over the substrate, the compositebarrier/etch stop layer comprising a lower silicon carbide (SiC) layerand an upper first oxygen doped SiC layer wherein the upper first oxygendoped SiC layer has a silicon content from about 25 to 35 atomic weight%, a carbon content of about 17 to 25 atomic wt. %, an oxygen content ofabout 5 to 15 atomic wt. %, and a hydrogen content from about 20 to 40atomic wt. %; a first dielectric layer formed over the upper firstoxygen doped SiC layer; an opening having sidewalls and a bottom, theopening extending through the first dielectric layer, the upper firstoxygen doped SiC layer and at least a portion of the lower SiC layer.14. An integrated circuit of claim 13, further comprising a conformaldiffusion barrier layer lining the sidewalls and the bottom of theopening and a metal layer formed on the diffusion barrier layer, themetal layer filling the opening.